Nuclear small-subunit ribosomal RNA gene sequences from representative Ceramiaceae (Ceramiales, Rhodophyta)

Recently published phylogenetic trees derived from nuclear small-subunit (SSU) ribosomal RNA gene sequences indicate particularly curious relationships for two species of the Ceramiaceae: Ceramium nodulosum and Griffithsia globulifera. To test these earlier results we have determined the SSU sequences for Anotrichium furcellatum, Ceramium macilentum, Crouania attenuata and Griffithsia monilis, all members of the Ceramiaceae, as well as for Gelidium pusillum of the Gelidiales. These are included in a multiple alignment containing representatives of all the ‘higher’ florideophyte orders. Our results indicate that an SSU sequence previously published for Griffithsia globulifera differs by only five nucleotide changes from a published gene for Gelidium vagum, as well as from the gene of Gelidium pusillum sequenced by ourselves. The two species of Gelidium differ from one another at four sites. In sharp contrast, our data for Griffithsia monilis strongly ally this species with other representative Ceramiales. The only other published ceramiacean SSU sequence, that of Ceramium nodulosum, allies only weakly, if at all, with the representative gene sequences available for members of the Dasyaceae, Delesseriaceae and Rhodomelaceae (Ceramiales) in phylogenetic analyses. Addition of the Ceramium macilentum gene to the multiple alignment strongly indicates monophyly for the Ceramiales (excluding G. globulifera) in all the phylogenies generated from the molecular data. We conclude that the lack of strength for a monophyletic Ceramiales in previous reports is largely attributable to the effects of the Ceramium nodulosum sequence on phylogenetic analyses.